RU2807589C1 - Controlled absorption screen - Google Patents

Abstract

FIELD: reduction of radar signature of antenna systems.

SUBSTANCE: controllable absorbing screen of the antenna system includes radio-transparent dielectric walls forming a sealed radio-transparent cavity, with the ability to control its properties of absorption of electromagnetic waves by filling the sealed radio-transparent cavity with absorbing liquid, while a membrane partition or corrugated structure is installed in the screen cavity, and elements of a frequency-selective structure are installed on its walls.

EFFECT: providing the ability to reduce the radar signature of antenna systems.

3 cl, 11 dwg, 1 ex

Description

The invention relates to radio engineering, in particular to a controlled absorbing screen, and can be used to reduce the radar signature of antenna systems.

To reduce the radar signature of antenna systems, screens made of frequency-selective surfaces are used, which are radio transparent in the frequency range of operation of antenna systems, and in other frequency ranges they either reflect or absorb electromagnetic radiation.

There is a known method for reducing the effective dispersion area of aperture antennas and phased antenna arrays of radar stations, which consists of installing a screen in the form of a conducting surface in the shape of a cone with slots cut in front of the antenna (Mikhailov G.D., Sergeev V.I. Methods and means of reducing radar signature of antenna systems. Foreign radio electronics, 1994, No. 4-5, pp. 54-59). This screen transmits electromagnetic waves with the frequency and polarization of its own radar station, and reflects electromagnetic radiation of other frequencies and polarizations. The disadvantage of this method and the device for its implementation is that the effective dispersion area of the antenna is reduced only at frequencies and polarizations different from those of the own radar station.

From patent RU 2469447 C2, published. 12/10/2012, Cl. H01Q 17/00, a controlled plasma screen is known, which is installed under a radio-transparent radome in front of the antenna sheet. When the electron concentration inside the screen is higher than a certain critical value in a certain frequency band, the screen becomes reflective and the effective dispersion area of the covered antenna can be significantly reduced. The disadvantage of this method is that a high-intensity mirror lobe is formed from the reflecting plasma screen, and in addition it is possible to form corner reflectors between the surface of such a screen and the structural elements in the antenna compartments (including the wall surface of the radio-transparent radome). The disadvantage of implementing this method is high power consumption, which is undesirable when used for an airborne radar station.

The technical problem to which the present invention is aimed is to reduce the radar signature of antenna systems, namely to create a controlled absorbing screen.

The technical result achieved by the invention is to reduce the radar signature of antenna systems.

This technical result is achieved through a controllable absorbing screen for antenna systems, which consists of radio-transparent dielectric walls forming a sealed radio-transparent cavity, with the ability to control the absorption properties of electromagnetic waves by filling the sealed radio-transparent cavity with absorbing liquid. Liquid dielectrics, in particular ethyl alcohol, acetone, methyl ethyl ketone, isopropanol, Lena coolant, tributyl phosphate, can be used as an absorbing liquid. A membrane partition or corrugated structure can be installed in the design of a controlled absorbing screen. Elements of a frequency-selective structure can be installed on the walls of the controlled absorbing screen.

The invention is illustrated by the following images:

Fig. 1 - controlled absorbing screen in a local vertical section;

Fig. 2 - design of a controlled absorbing screen with a membrane-type partition;

Fig. 3 - design of a controlled absorbing screen with a corrugated structure;

Fig. 4 - layout of a controlled absorbing screen;

Fig. 5 - dependence of the complex dielectric constant of ethyl alcohol on the frequency of electromagnetic radiation;

Fig. 6 - experimental frequency dependences of the transmission coefficient of a 10 mm thick alcohol layer in the “closed” mode;

Fig. 7 - experimental frequency dependences of the reflection coefficient of a 10 mm thick alcohol layer in the “closed” mode;

Fig. 8 - experimental frequency dependences of the transmission coefficient in the “open” mode without alcohol and with alcohol residues after the filling/draining cycle;

Fig. 9 - experimental frequency dependences of the reflection coefficient in the “open” mode without alcohol and with alcohol residues after the filling/draining cycle;

Fig. 10 - calculated frequency dependences of the transmission coefficient in the “closed” mode with a layer of alcohol of various thicknesses;

Fig. 11 - calculated frequency dependences of the reflection coefficient in the “closed” mode with a layer of alcohol of various thicknesses.

The following symbols are used in the images shown:

1 - radiotransparent dielectric walls;

2 - sealed cavity;

3 - absorbing liquid;

4 - filler;

5 - membrane partition;

6 - inlet fitting;

7 - outlet fitting;

8 - corrugated structure,

9 - frame,

10 - filling tube.

The controlled absorbing screen consists of radio-transparent dielectric walls 1, forming a sealed cavity 2, which is filled with absorbing liquid 3.

A controlled absorbing screen is installed in front of the antenna system. The cavity of the controlled absorbing screen is filled with absorbing liquid so that an absorbing volume is formed in which electromagnetic waves are absorbed, thereby reducing radar signature in a wide range of frequencies, including in the operating frequency range of the antenna covered by the control absorbing screen.

In fig. Figure 1 shows two states of the controlled absorbing screen “open” and “closed”.

In the “open” position, the sealed cavity 2 formed by radio-transparent dielectric walls 1 is not filled. In this position, the passage of electromagnetic waves through the cavity of the controlled absorbing screen is ensured.

When cavity 2 of the controlled absorbing screen is filled with absorbing liquid 3, an absorbing volume is formed. The absorbing liquid 3, filling the sealed cavity 2 between the radio-transparent dielectric walls 1, ensures the absorption of electromagnetic waves inside the cavity 2 of the controlled absorbing screen. In this way, the “closed” mode is implemented, which ensures the absorption of electromagnetic waves inside the screen volume and the reduction of radar signature in a wide range of frequencies in which radar stations operate, approximately in the range from 1 GHz to 15 GHz, including in the operating range covered by controlled antenna absorbing screen.

When the cavity 2 of the controlled absorbing screen is freed from the absorbing liquid 3, the “open” mode is again implemented, which ensures the passage of electromagnetic waves through the walls of the controlled absorbing screen.

As absorbing liquid 3, liquids with low values of dielectric constant and high values of the dielectric loss tangent in the required frequency range and a smooth dependence on frequency are used, i.e. liquids with high dielectric losses. Liquid dielectrics, such as ethyl alcohol, acetone, methyl ethyl ketone, isopropanol, Lena coolant, and tributyl phosphate can be used as absorbing liquid 3.

The thickness d of the absorbing liquid 3 is determined taking into account the dielectric characteristics of the liquid used, namely the values of dielectric constant and dielectric loss tangent, which are necessary to absorb electromagnetic radiation in the required frequency ranges and angles.

The walls of the controlled absorbing screen can be made in the form of dielectric sheathing, consisting of walls, inside of which a filler 5 is placed. The filler can be fiberglass, polystyrene foam, etc. Walls in the form of dielectric sheathing can be provided in the design of a controlled absorbing screen with a membrane-type partition with a corrugated structure (Fig. 2, 3).

A partition made of a membrane-type material may be located in the controlled absorbing screen. The design of a controlled absorbing screen with a membrane-type partition is shown in Fig. 2. The membrane-type partition is self-supporting and radiotransparent in the “open” mode. The filling of the controlled absorbing screen with absorbing liquid 3 is controlled by a membrane-type partition 6, while the absorbing liquid enters through the inlet fitting 7 and drains through the output fitting 8. The membrane partition 6 is located between the walls and pushes the liquid out of the cavity of the controlled absorbing screen.

An additional corrugated structure can be installed inside the controlled absorbing screen. The design of a controlled absorbing screen with a sealed cavity 2, inside of which a corrugated structure 9 is located, is shown in Fig. 3. The controlled absorbing screen with the corrugated structure 9 located inside the cavity 2 is also filled with absorbing liquid 3. The corrugated structure is evenly filled with the absorbing liquid and exerts distributed pressure on the walls of the controlled absorbing screen. The walls of the controlled absorbing screen are self-supporting and withstand the applied pressure, remaining radio-transparent in the “open” mode. Options for making a controlled absorbing screen with a corrugated structure provide structural rigidity and uniform distribution of fluid pressure on the walls of the controlled absorbing screen.

Conducting elements of a frequency-selective structure can be integrated into the design of the controlled absorbing screen, namely into its walls, which can provide an additional reduction in the effective dispersion area of the antenna, in the “open” state without absorbing liquid, without significantly reducing the technical characteristics of the antenna in the operating range frequency Frequency-selective elements are metal structures of various shapes and configurations. If the design of a controlled absorbing screen is made in such a way that electrically conductive elements of frequency-selective surfaces are integrated into its casing, then it is possible to further reduce the effective dispersion area of the antenna in the open state without absorbing liquid, without significantly reducing the technical characteristics of the antenna in the operating frequency range. The combined use of a controlled absorbing screen and frequency-selective surfaces will make it possible to combine the advantages of these camouflage means and obtain additional efficiency in measures to reduce the radar signature of the antenna.

The filling of the controlled absorbing screen is carried out using a screen filling control system. The screen filling control system includes a tank with absorbing liquid, a filling tube, a sensor for filling the cavity of the controlled absorbing screen with absorbing liquid, a pump and other parts and assemblies that ensure filling and draining of the absorbing liquid into the cavity of the controlled absorbing screen.

The controlled absorbing screen can have any shape and design and is not limited to the given example implementation.

The design of the walls of the controlled absorbing screen is determined based on the conditions for ensuring structural rigidity, tightness of the filled volume, and ensuring radio transparency in the “open” state without absorbing liquid. The selection of the optimal configuration of the wall structure should be made by calculating the frequency dependences of the transmission and reflection coefficient in the “open” mode, and the thickness of the layer of absorbing liquid d by calculating the transmission and reflection coefficient in the “closed” mode. For example, the method of integral equations and the method of equivalent long lines can be used for calculations (V.V. Bodrov, V.I. Surkov “Mathematical modeling of microwave devices and antennas.” Moscow, MPEI Publishing House. 1994 - 96 p.).

Example of implementation of the invention

As a prototype of a controlled absorbing screen, a sealed tank was assembled from two radio-transparent dielectric sheets mounted on a frame (Fig. 4). Radiotransparent dielectric sheets are the walls of 1 controlled absorbing screen. In fig. Figure 4 also shows a frame 9 on which the walls 1 of the controllable absorbing screen (radiotransparent dielectric sheets), the inlet fitting 6 and the filling tube 10 are fixed. In the “open” state, the controllable absorbing screen is transparent to electromagnetic waves.

The model of the controlled absorbing screen was filled with ethyl alcohol. Ethyl alcohol is an absorbing liquid with a low dielectric constant and a high dielectric loss tangent in the range from 1 GHz to 15 GHz, in which radar stations operate. The parameters (law of impedance change) of ethyl alcohol, selected as an absorbing liquid, are optimal from the point of view of using it as an absorber of electromagnetic waves.

In the “closed” state, the cavity of the mock-up of the controlled absorbing screen was filled with ethyl alcohol to a thickness of 10 mm.

In fig. Figure 5 shows the dependence of the complex dielectric constant of ethyl alcohol on the frequency of electromagnetic radiation. Using this dependence, it is possible to model the thickness of the absorbing liquid for the required frequency range of electromagnetic radiation and obtain the characteristics of reflection and transmission of electromagnetic radiation through the walls of the controlled absorbing screen.

In fig. 6, 7 show the results of measurements of the transmission coefficient and reflection coefficient of the layout of the controlled absorbing screen in the “closed” mode. The graphs above show that when the cavity of the controlled absorbing screen is filled with absorbing liquid, the transmission coefficient of electromagnetic waves does not exceed - 10 dB, while the reflection coefficient of electromagnetic waves is not higher than - 4 dB. Thus, by summing the reflected and absorbed electromagnetic waves, up to 80% of the electromagnetic wave power is absorbed using a controlled absorbing screen.

The measurement results of the transmission coefficient and reflection coefficient of the controlled absorbing screen model in the “open” mode without alcohol and with alcohol residues (alcohol film) on the inner surface of the walls are shown in Fig. 7, 8. Measurements with alcohol residues on the inner surface of the controlled absorbing screen mock-up were carried out after filling the sealed volume with alcohol and subsequent draining of the alcohol. At the same time, an alcohol film remained inside the structure, which reduced the transmission coefficient by minus 0.2 dB. Thus, there is a need to remove residual absorbing liquid after the fill/drain cycle to avoid deterioration of the radio performance in the "open" state.

In fig. 9, 10 show the calculated values of the transmission coefficient and reflection coefficient obtained by calculating the incidence of an electromagnetic wave on a flat wall of a mock-up of a controlled absorbing screen filled with alcohol of various thicknesses from 5 to 10 mm in increments of 1 mm. By calculation it is possible to estimate the minimum value of the alcohol layer to ensure the required level of absorption in the required frequency ranges and angular sectors. To do this, it is also necessary to use the dependence of the complex dielectric constant of ethyl alcohol on the frequency of electromagnetic radiation (Fig. 5). Using this dependence, it is possible to model a layer of absorbing liquid of a certain thickness for the required frequency range of electromagnetic radiation and the characteristics of reflection and transmission of electromagnetic radiation through the walls of a controlled absorbing screen.

To ensure filling and draining of the cavity of the controlled absorbing screen with absorbing liquid, as well as draining the walls of the controlled absorbing screen from the liquid film, a screen filling control system is used. The screen filling control system includes a tank with absorbing liquid, a filling tube, a sensor for filling the cavity of the controlled absorbing screen with absorbing liquid, a pump and other parts and assemblies that provide filling and draining of the absorbing liquid, such as a drive, such as solenoid valves, pipelines, pressure gauges, filters , check valves, etc.

When a command is given to fill the cavity of the controlled absorbing screen with absorbing liquid, the absorbing liquid is pumped from the tank into the cavity of the controlled absorbing screen; when the cavity is completely filled, according to a signal from the filling sensor, the inlet fitting closes, while the screen remains filled.

When a command is received to drain the absorbing liquid, the outlet fitting opens and the absorbing liquid is pumped from the cavity of the controlled absorbing screen into the tank. Upon completion of pumping, the cavity of the controlled absorbing screen is purged with air to completely dry and eliminate drops and films of absorbing liquid from the inner walls of the controlled absorbing screen.

The absorption screen can be controlled using compressed air (or nitrogen). In this case, the screen filling control system may consist of a tank divided by an impermeable membrane into two cavities for absorbing liquid and air, a cylinder (or several cylinders) for storing compressed air, reducers that reduce air pressure to pressurize the air cavity of the membrane tank, a set of electromagnetic taps with the help of which filling or removal of absorbing liquid is carried out, filling units (fittings, pressure gauges, filters, check valves) separately for charging with air and separately for filling with absorbing liquid, pressure alarms. To close the screen, an electrical signal is given to the electromagnetic valve, the valve opens, air from the cylinder passes through the reducer into the air cavity of the membrane tank, squeezing out the absorbing liquid. When completely filled, the pressure sensor stops the liquid supply process. To open the screen, a signal is sent to another electromagnetic tap. Air from the cylinders is supplied to the cavity of the controlled absorbing screen, squeezing the absorbing liquid back into the membrane tank. When the screen is completely freed from the absorbing liquid, the second pressure sensor gives a signal to the electromagnetic valve, which cuts off the liquid from the screen. Upon completion of pumping, the cavity of the controlled absorbing screen is purged using a purge system to free the cavity of the controlled absorbing screen from residual absorbing liquid, which can be discharged through drainage into the atmosphere.

The control system can be designed for repeated operation.

A controlled absorbing screen covers, in particular, aircraft antennas, providing absorption of electromagnetic waves, thus reducing the radar signature of the aircraft.

The use of a controlled absorbing screen to reduce the radar signature of antennas can be especially effective in cases where the diffraction lobes of the backscattering pattern of a covered antenna with a high level of effective scattering surface are located in probable directions of irradiation by the enemy at frequencies lying or located near the operating frequency range of the antenna.

In a situation where the diffraction lobes of the backscattering pattern of the protected antenna with a high level of effective scattering surface are formed in the operating frequency range of the protected antenna or near this range and are in the potential direction of irradiation by the enemy, then the use of simple frequency-selective screens is ineffective.

Claims (3)

1. A controlled absorbing screen of an antenna system, including radio-transparent dielectric walls forming a sealed radio-transparent cavity, with the ability to control its properties of absorption of electromagnetic waves by filling the sealed radio-transparent cavity with an absorbing liquid, while a membrane partition or corrugated structure is installed in the screen cavity, and on its walls there are elements of frequency-selective structure. 2. A controlled absorbing screen according to claim 1, in which liquid dielectrics are used as the absorbing liquid, in particular ethyl alcohol, acetone, methyl ethyl ketone, isopropanol, Lena coolant, tributyl phosphate. 3. A controlled absorbing screen according to claim 1, in which ethyl alcohol is used as the absorbing liquid.